There are known techniques for producing a chemical adsorbed film, including a casting method and a spin coating method. The casting method comprises lifting up a glass plate after immersing in a dilute solution of polymer material, removing an excessive portion of the solution from the glass plate which is placed upright, separating a film of the remaining polymer from the glass plate which is immersed into water, and placing the film onto a substrate. The spin coating method comprises applying a dilute solution of a polymer material onto a substrate and removing an excessive portion of the solution by spinning the substrate at a high speed so that the remaining of the polymer solution can form a film. Each method can however develop a film of as large as hundreds of angstroms in thickness.
An organic monomolecular film producing method for developing a thinner film at a molecular level of thickness is also provided, e.g. the Langmuir-Blodgett's method or another chemical adsorption film producing method using a chlorosilane surface-active agent. In particular, two such chlorosilane surface-active agents using the chemical adsorption film producing methods are depicted in Jacob Sagiv's report in the "Journal of American Chemical Society", Vol.102, p.92, 1980, and the report by K. Ogawa et. al. in "Langmuir", Vol.6, p.851, 1990 respectively.
The Langmuir-Blodgett's method comprises developing on a gas/water interface molecules having at end hydrophilic groups, reducing the area of molecule development to a minimum, and transferring the minimum size of the molecules onto a given substrate. The molecules rest vertically to the gas/water interface with their hydrophilic groups on the water side. The development of the molecules can be reduced to a minimum by pressing from one side of the gas/water interface with a tooling termed as a barrier. As the result, the molecules are arranged at high density thus forming a monomolecular film on the gas/water interface. The monomolecular film is then bonded to a substrate forming a Langmuir-Blodgett film. Repeating the foregoing procedure, involves accumulation of monomolecular films.
The chlorosilane surface-active agent using the chemical adsorption film producing method forms a monomolecular film using the chemical reaction between chlorosilyl groups bonded to the end of straight-chain hydrocarbon molecules and hydroxyl groups exposed on the substrate surface for removal of hydrogen chloride.
The monomolecular film developed by the Langmuir-Blodgett's method appears to be bonded to the substrate by means of van der Waals or Coulomb's force. The bonding strength between the film and the substrate is thus low, causing removal or dissolution of the film itself during processing.
The chlorosilane surface-active agent using the chemical adsorption film producing method is provided for solving the problem of low bonding strength, in which the developed monomolecular film is bonded to a substrate by an Si--O covalent bond resulting from dehydrochlorination and can exhibit a higher bonding strength sufficient to resist after-processing. However, the chlorosilane surface-active agent or any adsorbent used in the method provide higher activation and thus, has to be utilized in a non-water atmosphere such as a dry nitrogen gas. Also, such adsorbents are costly and their action of chemical adsorption takes as long as one or more hours.
A conventional chemical adsorption accumulated film producing method using a chlorosilane surface-active agent is disclosed in the report by K. Ogawa et. al. in "Langmuir", Vol.6, p.851, 1990, which comprises developing a monomolecular film on a substrate with the use of straight-chain hydrocarbon molecules which have at one end chlorosilyl groups and at the other end unsaturated bonds and serve as adsorbents, modifying the unsaturated bonds and releasing active hydrogen atoms by emission of electron beams, and repeating the preceding procedure for film accumulation. This method involves the emission of electron beams and thus requires a considerable size of beam emitter facility which will provide an unwanted risk and may cause damage to the film.